1. Field of the Invention
The present invention relates to a realistic robot mechanism which is constructed as a result of modeling the operation and mechanism of a living body, and, more particularly, to a legged mobile robot mechanism in which the mechanism of the body of a legged mobile animal, such as a human being and a monkey, is modeled.
Even more particularly, the present invention relates to a controlling mechanism of a legged mobile robot capable of getting up by itself when it has fallen down while walking or the like. Still more particularly, the present invention relates to a controlling method mechanism for a legged mobile robot which can get up by itself even when it has fallen down in various postures in order to automatically start to work again after the work has been interrupted because it has fallen down.
2. Description of the Related Art
A robot is a mechanical device which emulates the movement of a human being by making use of electrical and magnetic actions. The term robot is said to be derived from the Slavic word ROBOTA (slavish machine). In our country, the use of robots began from the end of the 1960s, many of which were industrial robots, such as manipulators and conveyance robots, used, for example, for the purpose of achieving automatic industrial operations in factories without humans in attendance.
In recent years, progress has been made in the research and development of legged mobile robots which emulate the movements and mechanisms of the body of an animal, such as a human being or a monkey, which walks on two feet while in an erect posture, so that there is a higher expectation of putting them into practical use. The posture and walking of legged mobiles which walk on two feet while in an erect posture are more unstable than those of crawler types or types having four or six legs, so that they are more difficult to control. However, the legged mobiles which walk on two feet while in an erect posture are excellent robots in that they can move and work flexibly because they can move along uneven surfaces such as unleveled surfaces and working paths having, for example, obstacles therein, and walk along walking surfaces which are not continuous, such as going up and down steps and ladders.
Legged mobile robots which emulate the mechanisms and movements of the bodies of human beings are called humanoid robots. Humanoid robots can, for example, help people in life, that is, help them in various human activities in living environments and in various circumstances in everyday life.
The significance of carrying out research and development on humanoid robots can be understood from, for example, the following two viewpoints.
The first viewpoint is related to human science. More specifically, through the process of making a robot whose structure which is similar to a structure having lower limbs and/or upper limbs of human beings, thinking up a method of controlling the same, and simulating the walking of a human being, the mechanism of the natural movement of a human being, such as walking, can be ergonomically understood. The results of such research can considerably contribute to the development of other various research fields which treat human movement mechanisms, such as ergonomics, rehabilitation engineering, and sports science.
The other viewpoint is related to the development of robots as partners of human beings which help them in life, that is, help them in various human activities in living environments and in various circumstances in everyday life. Functionally, in various aspects of the living environment of human beings, these robots need to be further developed by learning methods of adapting to environments and acting in accordance with human beings which have different personalities and characters while being taught by human beings. Here, it is believed that making the form and structure of a robot the same as those of a human being is effective for smooth communication between human beings and robots.
For example, when teaching to a robot a way of passing through a room by avoiding obstacles which should not be stepped on, it is much easier for the user (worker) to teach it to a walking-on-two-feet-type robot which has the same form as the user than a crawler-type or a four-feet-type robot having completely different structures from the user. In this case, it must also be easier for the robot to learn it. (Refer to, for example, “Controlling a Robot Which Walks On Two Feet” by Takanishi (Jidosha Gijutsukai Kanto Shibu <Koso> No. 25, April, 1996.)
The working space and living space of human beings are formed in accordance with the behavioral mode and the body mechanism of a human being which walks on two feet while in an upright posture. In other words, for moving present mechanical systems using wheels or other such driving devices as moving means, the living space of human beings has many obstacles. However, it is preferable that the movable range of the robot is about the same as that of human beings in order for the mechanical system, that is, the robot to carry out various human tasks in place of them, and to deeply penetrate the living space of human beings. This is the reason why there are great expectations for putting a legged mobile robot into practical use. In order to enhance the affinity of the robot to the living environment of human beings, it is essential for the robot to possess a human form.
One application of humanoid robots is to make them carry out various difficult operations, such as in industrial tasks or production work, in place of human beings. They carry out in place of human beings dangerous or difficult operations, such as maintenance work at nuclear power plants, thermal power plants, or petrochemical plants, parts transportation/assembly operations in manufacturing plants, cleaning of tall buildings, and rescuing of people at places where there is a fire, and the like.
The most important theme is to design and manufacture industrial robots so that they can be industrially used as specified and can provide the specified functions. Industrial robots are constructed on the assumption that they walk on two feet. However, as mechanical devices, they do not necessarily have to faithfully reproduce the actual body mechanisms and movements of animals, such as human beings or monkeys, which walk while they are in an erect posture. For example, in order to produce an industrial robot for a particular use, the degree of freedom of the movement of particular parts, such as the finger tips, and their operational functions are increased and enhanced, respectively. On the other hand, the degrees of freedom of parts which are considered comparatively unrelated to a task, such as the head, the trunk (the backbone, etc.), and the waist, are limited in number or are not provided. This causes the industrial robot to have an unnatural external appearance when it works and moves, although it is a type of robot which walks on two feet. However, a compromise is inevitable.
Another application of humanoid robots is related to closely connecting them to life, that is, “to the living together with human beings” rather than helping them in life by carrying out difficult tasks in place of human beings. In other words, the ultimate purpose is to make these robots faithfully reproduce whole body harmoniously moving type operation mechanisms which animals, such as human beings and monkeys, which walk on two feet while they are in an erect posture actually have, and to make them move naturally and smoothly. In addition, in emulating highly intelligent animals, such as human beings or monkeys, which stand in an upright posture, an operation using the four limbs is natural for a living body, and it is desirable that the movements are sufficiently indicative of emotions and feelings. Further, the humanoid robot is required not only to faithfully execute a previously input operation pattern, but also to act vividly in response to the words and actions of a person (such as speaking highly of someone, scolding someone, or hitting someone). In this sense, entertainment robots which emulate human beings are rightly called humanoid robots.
As is already well known in the related art, the human body has a few hundred joints, that is, a few hundred degrees of freedom. In order to make the movements of legged mobile robots as close to those of human beings, it is preferable that the legged mobile robots be allowed to virtually have about the same number of degrees of freedom as human beings. However, this is technologically very difficult to achieve. This is because, since at least one actuator needs to be disposed to provide one degree of freedom, a few hundred actuators need to be disposed for a few hundred degrees of freedom. This is impossible to achieve from the viewpoints of production costs and their weight and size and other designing factors. In addition, when the number of degrees of freedom is large, the number of calculations required for, for example, positional/operational control or stable posture control operation is correspondingly increased exponentially.
Accordingly, a humanoid robot is in general constructed so as to possess about a few tens of degrees of freedom at the joints which is far less than that possessed by the human body. Therefore, it can be said that how to achieve natural movement using few degrees of freedom is one important factor in designing/controlling a humanoid robot.
For example, that a flexible mechanism such as a backbone is important for various complicated movements in the life of human beings is already apparent from the viewpoint of ergonomics. The value of existence of the degree of freedom at the trunk joint which signifies the backbone is low, but it is important for entertainment robots and other humanoid robots which are closely connected to life. There is a demand that the flexibility of the robot be capable of being actively adjusted in accordance with the condition.
Legged mobile robots which walk on two feet while they are in an erect posture are excellent robots in that they can walk and move flexibly (such as up and down steps or over obstacles). However, since the number of legs is decreased and the center of gravity of such robots is located at a high position, it becomes correspondingly difficult to perform posture control and stable walking control operations. In particular, in the case of closely connected to life type robots, the walking and the posture of the whole body need to be controlled while they move naturally and in a way sufficiently indicative of emotions and feelings of intelligent animals, such as human beings or monkeys.
Many techniques regarding stable walking control operations and posture control of a legged mobile robot which walks on two feet have already been proposed. Here, stable “walking” means to move using the legs without falling down.
Stable posture control operation of a robot is very important in preventing the robot from falling down. This is because the falling down of the robot means interruption of the execution of the task of the robot, and the need of considerable labor and time for starting the execution of the task again after the robot has got up from its “fallen-down state.” Above all, when the robot falls down, the robot itself or the object with which it collides when it falls down may be fatally damaged. Therefore, carrying out a stable posture control operation or preventing the robot from falling down when it is walking is one important factor.
When the robot is walking, the acceleration which is produced when the robot walks and by the gravitational force causes a gravitational force, an inertial force, and the moment of these two forces to act on the surface of a path from the walking system. According to the so-called “d'Alembert's principle,” these balance with the floor reaction force and the floor reaction force moment which react in an opposite direction from the surface of the path to the walking system. From the theory of mechanics, it is inferred that there exist a point where the pitch axis moment and the roll axis moment become zero on or within a side of a supporting polygonal form formed by the surface of the path and the points where the soles contact the floor. In other words, a ZMP (zero moment point) exists.
Many of the proposals made to prevent a legged mobile robot from falling down while it is walking or to perform a stable posture control operation on the robot use the ZMP as a standard for determining the walking stability. The generation of a pattern for walking on two feet based on the ZMP as a standard has the advantage of allowing previous setting of the points where the soles contact the floor, making it easier to take into consideration the kinematical limiting conditions of the toes in accordance with the form of the surface of a path.
For example, Japanese Unexamined Patent Publication No. 5-305579 discloses a walking controller of a legged mobile robot. The walking controller disclosed in this document performs a controlling operation so that the ZMP (zero moment point), that is, the point on the floor surface where the moment resulting from the reaction force of the floor when the robot walks is zero matches a target value.
Japanese Unexamined Patent Publication No. 5-305581 discloses a legged mobile robot constructed so that the ZMP is either situated in the inside of a supporting polyhedral (polygonal) member or at a location sufficiently separated by at least a predetermined amount from an end of the supporting polyhedral (polygonal) member when a foot of the robot lands on or separates from the floor. As a result, even when the robot is subjected to an external disturbance, the sufficient predetermined distance of the ZMP makes it possible to cause the robot to walk more stably.
Japanese Unexamined Patent Publication No. 5-305583 discloses the controlling of the walking speed of a legged mobile robot by a ZMP target location. More specifically, in the legged mobile robot disclosed in this document, previously set walking pattern data is used to drive a leg joint so that the ZMP matches a target location, and the tilting of the upper part of the body is detected in order to change the ejection speed of the set walking pattern data in accordance with the detected value. Thus, when the robot unexpectedly steps on an uneven surface and, for example, tilts forward, the original posture of the robot can be recovered by increasing the ejection speed. In addition, since the ZMP can be controlled so as to match the target location, there is no problem in changing the ejection speed in a device for supporting both legs.
Japanese Unexamined Patent Publication No. 5-305585 discloses the controlling of the landing position of a legged mobile robot by a ZMP target location. More specifically, the legged mobile robot disclosed in this document is made to walk stably by detecting any shifts between the ZMP target location and the actually measured position and driving one or both legs so as to cancel the shift, or by detecting the moment around the ZMP target location and driving the legs so that it becomes zero.
Japanese Unexamined Patent Publication No. 5-305586 discloses the controlling of the tilting of the posture of a legged mobile robot by a ZMP target location. More specifically, the legged mobile robot disclosed in this document is made to walk stably by detecting the moment around the ZMP target location and driving the legs so that, when the moment is being produced, the moment is zero.
The greatest effort should be made to previously prevent the robot which is walking from falling down. However, the research of robots which walk on two feet or which have a small number of legs is only at a stage in which the first step towards putting them into practical use has been finally started, so that the possibility of such robots falling down cannot be reduced to zero.
Therefore, in order to put the legged mobile robots into practical use at an early stage, it is important not only to take measures to previously prevent the robots from falling down, but also to minimize damages which result when the robots fall down and to more reliably cause them to start working again, that is, to more reliably cause them to get up or stand up.
In human living environments where there are various obstacles and unexpected situations, the robot cannot be prevented from falling down. In the first place, human beings themselves fall down. Therefore, it is no exaggeration to say that, in order to completely automate the robot, it is essential for the legged mobile robot to include an operation pattern for independently getting up from its fallen-down state.
For example, Japanese Unexamined Patent Publication No. 11-48170 treats the problem of a legged mobile robot falling down. However, this document proposes to reduce to the extent possible damages to the robot itself and to the object with which the robot collides by moving the center of gravity of the robot downward when the robot is about to fall down. Therefore, it discusses nothing about increasing the reliability with which the robot starts operating again after it has fallen down, that is, the reliability with which the robot gets up or stands up.
Even if the robot is described as simply “falling down,” the robot takes various postures after it has fallen down. For example, for a bipedal legged mobile robot, there are a plurality of “fallen-down postures” which include a “lying-on-the-face posture,” a “lying-on-the-back posture,” and a “lying sideways posture.” Constructing a robot so that it can only get up from some of these fallen-down postures (for example, from only the “lying-on-the-face posture”) is not enough in claiming the construction of a robot which gets up independently and which is completely automated.
For example, a legged mobile robot shown in FIG. 35 will be considered. The robot shown in this figure is a humanoid robot which walks on two feet in an upright posture, and comprises a head, a trunk, lower limbs, and upper limbs. The legs possess the degrees of freedom required for walking, and the arms possess the degrees of freedom required for its supposed tasks. For example, each leg possesses six degrees of freedom, while each arm possesses four degrees of freedom. The trunk is the center of the structural member and connects the legs and arms, and the head. However, the trunk of the robot shown in the figure possesses zero degrees of freedom.
In general, the legged mobile robot walks as a result of relative movements between the portions of the legs which contact the floor and center point of the dynamic moment or the center of gravity. When the robot is a type which walks on two feet, movement in a predetermined direction is achieved by alternately placing the left and right legs in a “standing state” and a “swinging state.” Here, it is basically necessary to move the center of the dynamic moment or the center of gravity of the body towards the “standing state” side, and in a predetermined direction of movement. In the legged mobile robot, these movements are achieved by harmonious actuation which is achieved by the degrees of freedom at the joints of the portions of the robot. When the legged mobile robot has legs each possessing six or more degrees of freedom, such as the robot shown in FIG. 35, the center of the dynamic moment or the center of gravity of the body when the robot is walking can be moved as a result of the degrees of freedom of the legs.
FIG. 36 shows a state in which the legged mobile robot shown in FIG. 35 is in an upright state. In this upright posture, the center of gravity of the robot as viewed from the direction of the front side of its body is above the center portions of both legs, and the ZMP is situated within a stable posture area, substantially midway between the portions of both legs which contact the floor.
FIG. 37 shows a state in which the center of gravity is moved to one of the legs (the left leg in the figure) to allow the legged mobile robot to walk. In other words, the ZMP is moved to within an area where the left foot contacts the floor by moving the center of gravity of the robot towards the left leg as a result of movement primarily involving a displacement of a left hip joint and a displacement of a left ankle joint in a roll direction, and a corresponding displacement of a right hip joint and a corresponding displacement of a right ankle joint in the roll direction. As a result, the robot takes a posture which can support the whole weight of the body only by the left leg. In addition, the robot can walk by stepping forward in a desired direction of movement its right leg which is in a “swinging state.”
A bipedal legged mobile robot which is primarily assumed to walk can walk using only the degrees of freedom of the legs depending on the degree-of-freedom arrangement. Such a walking operation pattern is often used in actual machines. In addition, in order to perform tasks, the robot is generally constructed so as to possess separate degrees of freedom at the arms and hands. Further, the head often possesses degrees of freedom for visual perception and the like.
In contrast, it cannot be said that the degrees of freedom of the trunk are required for an operation pattern for primarily causing the robot to walk or perform tasks. Therefore, the trunks of most of the legged mobile robots which are presently being developed for practical purposes do not possess any degrees of freedom, as shown in FIG. 35 (discussed above).
A getting-up operation of a legged mobile robot which does not possess degrees of freedom at the trunk, such as that shown in FIG. 35, when the robot has fallen down will be considered.
For example, when the robot is to get up from the “lying-on-the-face posture” such as that shown in FIG. 38, actuation is performed at the pitch axes of both hip joints and both arms, etc., in order to cause only the arms and legs (knees) to contact the floor. Then, the relative distances between portions of the arms and corresponding portions of the legs which contact the floor are gradually decreased in order to move the center of gravity of the robot upward (see FIG. 39).
The feet are moved forward (see FIG. 40) at the same time that the center of gravity is moved upward. As a result, the center of gravity moves above an area where the feet contact the floor, and the ZMP moves into a floor contacting area, that is, a stable posture area, making it possible to move the arms off the surface of the floor (see FIG. 41). In addition, by extending the legs (knee joints) in order to move the center of gravity upward, the getting-up operation is completed (see FIG. 42).
However, since problems regarding interference between the portions of the robot and the movement angle of each joint exist, it is often the case that the center of gravity cannot be moved sufficiently. For example, when changing from the posture shown in FIG. 40 to that shown in FIG. 41, the knees cannot be sufficiently bent while the arms are in contact with the floor, making it impossible to move the ZMP to the area where the feet contact the floor. When an attempt is made to forcibly move the ZMP to the area where the feet contact the floor, the arms move off the floor before the ZMP moves into the stable area, so that the robot cannot get up properly.
When, as shown in FIG. 43, the legged mobile robot falls down in the lying-on-the-back posture, it is even more difficult for the robot to get up independently, that is, without any physical help from the outside.
When carrying out a getting-up operation from the lying-on-the-back posture, the robot is first made to take a posture in which it contacts the floor with the legs and arms in order to move the center of gravity upwards (see FIG. 44). Then, the relative distances between the portions of the feet which contact the floor and the corresponding portions of the arms which contact the floor are gradually decreased (see FIG. 45).
When the relative distances between the feet and the corresponding arms are made sufficiently small, the center of gravity of the robot can be moved to above the area where the feet contact the floor (see FIG. 46). In this state, the ZMP enters within the feet or stable posture area, so that, by moving the arms off the surface of the floor, and extending the legs, that is, the knees in order to move the center of gravity further upwards, the getting-up operation is completed (see FIG. 47).
However, actually, problems such as interference between portions of the robot and the movement angle of each joint exist as with the case where the robot gets up from the lying-on-the-face state, so that there are many times when the center of gravity cannot be sufficiently moved. For example, when the posture changes from that shown in FIG. 45 to that shown in FIG. 46, the knees cannot be sufficiently bent while the arms are in contact with the floor, so that the ZMP cannot be moved to the area where feet contact the floor. When an attempt is made to forcibly move the ZMP, the arms move off the ground before the ZMP moves into the stable area, so that the robot cannot get up properly.
In the cases where the getting-up operation from the lying-on-the-face posture shown in FIGS. 38 to 42, and from the lying-on-the-back posture shown in FIGS. 43 to 47 are executed, the angles of movements of the hip joints towards the front side of the body are increased in order to make it possible to prevent a bottleneck shown in FIGS. 40 and 41 and FIGS. 46 and 47. However, in order to increase the angles of movements of the hip joints of the actual legged mobile robots, interference occurs between the trunk and the portions therearound, so that it cannot be said that this actually solves the problems.
In the cases where the getting-up operations from the lying-on-the-face posture and from the lying-on-the-back posture are executed, when the center of gravity of the whole legged mobile robot is set near the feet by constructing very heavy feet, the ZMP can be moved to the stable posture area even when the arms move off the ground first as shown in FIGS. 41 and 47. This is similar to the principle on which a “daruma” naturally gets up.
In the case where a “static walking type” robot in which the center of gravity thereof is always within the area where the soles contact the floor while it is walking, it is possible to ensure stable walking even when, as in a “daruma,” the center of gravity of the whole robot is situated at a low place such as at the feet.
In contrast, in the case of a “dynamic walking type” robot in which the center of gravity of the robot is situated outside the area of the soles, the posture of the robot is restored by greatly accelerating a fulcrum in the direction in which the robot has fallen down while the robot is walking, so that the concept of an “inverted pendulum” is made use of. In other words, in the case of the “dynamic walking type” robot, in order to allow dynamic movement of the center of gravity, the legs are designed to be relatively light with respect to the condition such that the center of gravity is situated at a relatively high place. On the other hand, when the mass of each leg is large, it becomes difficult to move the center of gravity smoothly, so that the walking of the robot is hindered. To recapitulate, setting the center of gravity of the whole robot at a low place makes it difficult to perform a stable posture control operation when it is walking dynamically, so that what has been mentioned above cannot be a general solution for a legged mobile robot which gets up.
As can be seen from FIGS. 38 to 42 and from FIGS. 43 to 47, when a legged mobile robot which does not possess any degrees of freedom at the trunk is used, the amount of movement of the arms, head, etc., and legs relative to each other are small, making it difficult for the robot to get up from either one of the fallen-down postures.
By forming the trunk of the robot very short, or by forming the arms very long, the amount of movement between the arms and legs relative to each other can be increased. This eliminates the problem of the arms moving off the floor before the ZMP moves into the stable posture area as shown in FIGS. 41 and 47, making it possible for the robot to get up.
However, when the trunk is made short or the arms are made long, the four limbs or the whole body of the humanoid robot is no longer proportioned, thereby departing from the spirit of the invention of producing a human-like or humanoid robot.
At the time this application was filed, there was a tendency to frequently install a unit for controlling the robot itself at the back side portion thereof. Therefore, when the robot fell down in the laying-on-the-back posture, the center of gravity greatly shifted towards the back surface side thereof. Accordingly, it was supposed even more difficult for such a robot to get up from the lying-on-the-back posture (see FIG. 48).